OLEDs having increased illumination are disclosed. The OLEDs have light emitting layers with periodic grain sizes. In particular, by depositing smaller particles at the boundaries of the emitting layers, the injection rate of carriers is improved in the emitting layers and by depositing larger particles in the middle of the emitting layers, the carrier density is increased, which increases electron-hole recombination. Increased recombination facilitates radiative emission of exitons from the OLED. As a result of the periodic grain size structure of the emitting layers, the electroluminescence and durability of the OLEDs are improved.